In a multi-cylinder reciprocating internal combustion engine, there are differences in the amount of useful torque produced by each cylinder, even during normal operation. Small between-cylinder torque differences can cause rough idling and poor emissions performance. Large between-cylinder differences can cause extremely rough operation and may indicate faulty cylinder and/or fuel injection components. The process of sensing these torque differences and using the information for compensation or diagnosis of engine operation is known as cylinder balancing.
Most present day electronically controlled engines include some form of interrupt-based engine speed sensing mechanism, which allows measurement of engine speed at very short intervals. Although there have been prior art systems which infer engine torque changes from this data in order to balance cylinder output power, they have generally proven to be unsatisfactory. There is therefore a need for a method and apparatus for engine cylinder balancing using sensed engine speed which allows real time control of cylinder fueling in order to continuously balance engine cylinder power contribution. The present invention is directed toward meeting this need.